1. Field of the Invention
This invention is directed generally to an injection nozzle assembly. More particularly, this invention is directed to a heated plastic flow control nozzle assembly for use in plastic molding which significantly reduces drool upon separation of the nozzle assembly from a mold or hot runner.
2. Description of the Prior Art
The use of plastic products has become widespread in all industries today. A typical molded part is made by filling a mold cavity with pressurized molten plastic, allowing the plastic to cool, and removing the molded article from the mold cavity. It is important in injection molding processes to control the flow of the resinous material in order to avoid the waste of material which increases operating costs and reduces profits.
A typical plastic injection machine nozzle engages a mold or a hot runner system associated with the mold. Before the mold halves are separated to permit removal of the molded plastic part, the nozzle must be separated from the hot runner or mold. This separation withdraws the nozzle from its seat in the mold or the runner and the molten plastic in the nozzle is apt to drool out. Such drool results not only in a loss of material but can cause problems in the molding process. For example, the drooling hot plastic is apt to run out into the runner system or into the mold after the part is removed. Such plastic accumulation may adversely affect the operation of the mold by not permitting the mold to close properly or inhibit proper heat exchange during cooling of the mold. Further, such drooling may result in partial voids in the runner system leading to incomplete mold cavity charging.
Various controls have been proposed to control the shutoff nozzle to attempt to eliminate drool. In U.S. Pat. No. 2,318,031 issued to Tucker, one type of nozzle shutoff is disclosed. Here, the nozzle utilizes a rotary valve mounted at the output of the nozzle itself. This valve in turn, is rotated by a hydraulic motor which disconnects a passage through the valve body to disconnect the flow of plasticized resin. Another valve method is shown in this patent wherein the opening of the nozzle is accomplished by a pure mechanical means. Here a valve closure has a rod connected to the valve protruding from the end of the nozzle. As the mold is closed, the rod engages the mold surface and opens the valve to allow material to flow into the mold. As the mold is opened the valve will shutoff from the pressure of the resin inside the unit.
U.S. Pat. No. 3,231,938 issued to Seymour, shows a spring operated nozzle means wherein the flow of plasticized resin will increase the pressure in the nozzle and cause the shut-off to be pushed against the spring, thus opening the entrance to the mold. Upon completion of the injection step, the pressure of the resin will be reduced and the spring will push the shutoff member back into its original position thereby disconnecting the flow of plasticized resin to the mold. Another U.S. Pat. No. 3,241,191 issued to Nouel, shows a spring-lever type mechanical method for operating the shutoff valve whereby resin under pressure forces the nozzle shutoff to a mid-position acting to regulate the flow of resin through the tip of the nozzle. The valve is double acting and when the mold is filled, the pressure of the resin inside the mold will force back the shutoff through a mechanical arm against a spring which shuts off the flow of resin to the mold. Here the flow of resin and spring biasing means are used to open and return the valve to its shutoff position.
U.S. Pat. No. 3,571,856 issued to Voelker, shows a shutoff means whereby the control is by a hydraulic actuator which is connected to a rod inside a ball and socket connected to a manifold means having an orifice opening into the mold. The rod is capable of being moved to open or shutoff the orifice to the mold. The rod operates as a valve to disconnect plasticized resin from flowing through the nozzle means through the orifice into the mold cavity.
Another means of shutting off or disconnecting the flow of plasticized resin through a nozzle is shown in U.S. Pat. No. 3,902,665 issued to Hendry. This patent discloses various nozzle shut-off means being operated by a fluid pressure to stop the flow of plasticized resin from the extruder into the nozzle itself. Here, the opening and closing of the nozzle shut-off means can be by a fluid means or the opening of the shut-off can be caused by the force of plasticized resin against the shut-off rod pushing the valve back to its seated position. The return to a closed position is by a compressed air or fluid means. U.S. Pat. No. 3,649,148 issued to Waltman, shows a means for controlling the orifice of a nozzle which operates using a fluid means to control the wall thickness of plasticized resin as it is extruded from the nozzle in the manufacture of blow molded bottles.
Rogers et al., U.S. Pat. No. 5,012,839, discloses a flow control valve intended to be used primarily with a hot runner manifold in a mold of a molding press to prevent plastic drool or seepage when the molten plastic injection nozzle is separated from the mold. The heated plastic flow control valve assembly disclosed utilizes a slide valve which is telescopingly slidable with respect to a valve body to provide positive flow control for molten plastic. The slide valve has a central plastic flow passage whose discharge openings are closed when the discharge end of the slide valve telescopes within the valve body. A coil spring surrounds the slide valve and provides the valve closing force. The body of the valve assembly is surrounded by a band heater while the sprue core portion of the valve assembly, which cooperates with the hot runner manifold in the mold, is provided with a coil heater. These two heaters are individually controllable to ensure that the plastic material in the valve assembly is kept at the proper temperature.
As can be seen from the above discussion of the prior art, what is needed is a nozzle assembly which will prevent plastic seepage or drooling of plastic material, thereby avoiding adverse operation of the molding process, reduce down time and loss of costly material.